Acute and Chronic Toxicity of Sodium Nitrate and Sodium Sulfate to Several Freshwater Organisms in Water‐Only Exposures

Elevated nitrate (NO₃) and sulfate (SO₄) in surface water are of global concern, and studies are needed to generate toxicity data to develop environmental guideline values for NO₃ and SO₄. The present study was designed to fill existing gaps in toxicity databases by determining the acute and/or chronic toxicity of NO₃ (tested as NaNO₃) to a unionid mussel (Lampsilis siliquoidea), a midge (Chironomus dilutus), a fish (rainbow trout, Oncorhynchus mykiss), and 2 amphibians (Hyla versicolor and Lithobates sylvaticus), and to determine the acute and/or chronic toxicity of SO₄ (tested as Na₂SO₄) to 2 unionid mussels (L. siliquoidea and Villosa iris), an amphipod (Hyalella azteca), and 2 fish species (fathead minnow, Pimephales promelas and O. mykiss). Among the different test species, acute NO₃ median effect concentrations (EC50s) ranged from 189 to >883 mg NO₃‐N/L, and chronic NO₃ 20% effect concentrations (EC20s) based on the most sensitive endpoint ranged from 9.6 to 47 mg NO₃‐N/L. The midge was the most sensitive species, and the trout was the least sensitive species in both acute and chronic NO₃ exposures. Acute SO₄ EC50s for the 2 mussel species (2071 and 2064 mg SO₄/L) were similar to the EC50 for the amphipod (2689 mg SO₄/L), whereas chronic EC20s for the 2 mussels (438 and 384 mg SO₄/L) were >2‐fold lower than the EC20 of the amphipod (1111 mg SO₄/L), indicating the high sensitivity of mussels in chronic SO₄ exposures. However, the fathead minnow, with an EC20 of 374 mg SO₄/L, was the most sensitive species in chronic SO₄ exposures whereas the rainbow trout was the least sensitive species (EC20 > 3240 mg SO₄/L). The high sensitivity of fathead minnow was consistent with the finding in a previous chronic Na₂SO₄ study. However, the EC20 values from the present study conducted in test water containing a higher potassium concentration (3 mg K/L) were >2‐fold greater than those in the previous study at a lower potassium concentration (1 mg K/L), which confirmed the influence of potassium on chronic Na₂SO₄ toxicity to the minnow. Environ Toxicol Chem 2020;39:1071–1085. © 2020 SETAC